DESCRIPTION: The goals of this application are to clone the gene for preaxial polydactyly type 2 (PPD2), and to determine the role of PPD2 in limb development. Patients with PPD have a polydactyly of the thumbs, fingers or toes. Specifically, PPD2 results in polydactyly of the thumbs and duplication of the big toe. PPD is inherited as an autosomal dominant with variable expressivity. Preliminary work by this investigator, and collaborators, have demonstrated linkage of PPD2 to a 5 cM region in 7q36. The specific aims of this application are: 1. To collect additional family members from a large pedigree currently being analyzed, and to collect new PPD2 pedigrees and confirm they link to 7q31. 2. Develop new microsatellite markers from this region to refine the localization of PPD2. 3. Identify candidate PPD2 genes from this refined region. 4. Analyze patterns of expression of genes from the minimal region to see if they are expressed appropriately during development to be candidate PPD2 genes. 5. Mutation analysis of candidate genes to identify the correct PPD2 gene.